oracle--merge

MERGE语句是Oracle9i新增的语法，用来合并UPDATE和INSERT语句。

MERGE INTO [your table-name] [rename your table here]
USING ([write your query here])[rename your query-sql or using just like a table]
ON ([conditional expression here] AND [...]...)
WHEN MATHED THEN [here you can execute some update sql or something else ]
WHEN NOT MATHED THEN [execute something else here ! ]

oracle10g后对merge做了一些改动：

1、UPDATE或INSERT子句是可选的

when mathed和when not mathed不必都写上，可以只用when mathed，也可以只用when not mathed

2、UPDATE和INSERT子句可以加WHERE子句
3、在ON条件中使用常量过滤谓词来insert所有的行到目标表中,不需要连接源表和目标表

例如：merge into products p using (select * from newproducts) np on (1=0).......
4、UPDATE子句后面可以跟DELETE子句来去除一些不需要的行

给一个例子：

<update id="updateOrderInfo" parameterClass="com.edai.pojo.EntityForBuyEPlan">
MERGE INTO t_cus_order O
USING dual
on (user_id= #userId# and PRODUCT_TYPE=#productType#)
WHEN MATCHED THEN
       update  set  
       INVEST_AMOUNT = INVEST_AMOUNT+#amount#,
       LAST_UPDATE_DATE = systimestamp,
       UPDATE_PER = 'HOUPURCHASE',
       ASSIGNMENT_STATUS ='2',
       CASH_VALUE = CASH_VALUE+#amount#,
       FROZEN_IDLE_FUNDS=FROZEN_IDLE_FUNDS+#amount#,
       ORDER_VALUE = ORDER_VALUE + #amount# 
WHEN NOT MATCHED THEN 
           insert  
          (
            O.ORDER_ID,
            O.ACCT_ID,
            O.USER_ID,
            O.CREDIT_ACCT_ID,
            O.CASH_VALUE,
            O.INVEST_DATE,
            O.LOCK_TIME,
            O.INVEST_AMOUNT,
            O.FROZEN_IDLE_FUNDS,
            O.FROZEN_PRE_MATCH_FUNDS,
            O.FROZEN_HAS_MATCH_FUNDS,
            O.PRODUCT_TYPE,
            O.ORDER_STATE,
            O.CREATE_DATE,
            O.CREATE_PER,
            O.CYCLE_MATCH_TYPE,
            O.BUY_MEDIA,
            O.ASSIGNMENT_STATUS,
            O.ORDER_VALUE
          ) values(        
                  SEQ_ORDER_NUM.NEXTVAL,
                  (select acct_id from t_cus_acct where user_id = #userId#    ), 
                  #userId#,
                  (select credit_acct_id from t_cus_acct_credit where user_id = #userId# and product_type = #productType#),
                  #amount#,
                  systimestamp,
                  (select fp.base_lock_period from finance_plan@db_link_bl fp where fp.id=#productType#),
                  #amount#,
                  #amount#,
                  '0',
                  '0',
                  #productType#,
                  #orderState#,
                  systimestamp,
                  'HOUPURCHASE',
                  #cycleMatchType#,
                  #buyMedia#,
                  '2',
                  #amount#
          )
</update>